1. Field of the Invention
The present invention relates to a processing device for comminuting, conveying and plasticizing of thermoplastic synthetic material comprising a conveying device, a comminuting device and a screw-type extrusion machine.
2. Brief Description of the Background of the Present Invention Including Prior Art
It is known to comminute plastic material in a grinder and to transport the plastic material into a silo, from which silo the pre-comminuted plastic material is then fed through a tamping device to an extruder, the latter being in most cases a screw-type extrusion machine. This configuration has the advantage that the silo offers a storage capacity by way of which fluctuations in the production of material can be balanced.
On the other hand, a disadvantage of this configuration is its poor thermal efficiency, since the comminuting energy, which is transferred in the grinder in the form of frictional heat onto the plastic material, is again discharged to the surroundings based on the subsequent intermediate storage in the storage silo and thus is lost for the extrusion process. In addition this configuration has the disadvantage, that it requires a considerable amount of space and its construction is very costly.
An apparatus has become known from the printed patent document WO 98/07042, where the material to be processed falls from the top into a container, at the floor of which a cutter disk rotates, the cutter disk pre-comminuting the material and pressing it into an opening disposed in the container wall, where a screw-type extrusion machine receives the material.
An arrangement of this type has the advantage that the comminuting energy that is imparted to the material to be processed in the form of frictional heat can be employed in the extrusion process. However, very substantial disadvantages exist, because this arrangement can only be fed with material particles of limited size and the feeding always has to be performed uniformly, since otherwise the drive motor can be overloaded or the plastic material still in the container can melt down, which may cause clogging or may cause the cutter disk to jam. Therefore, the material to be processed always has to be conveyed into the charging bin in small pieces and at a uniform speed.
However, this necessitates a process of separating the comminuted material according to the size of each piece, which proves to be expensive and complicated, in particular in the case of pressed plastic material or in the case of large solid parts that have to be separated either manually or automatically, requiring a substantial expenditure of labor or an additional substantial investment expenditure in the form of a coarse crushing machine.
Further known is an apparatus for the processing of thermoplastic synthetic material and filler material such as sawdust, for example. With this apparatus, mainly humid material is to be pre-dried and then to be conveyed into an extruder. As a disadvantage of this arrangement, the size of the material that is suitable for feeding to the apparatus is limited, given that here, again, the material falls into a charging funnel by gravity and, in case of oversized pieces of material, the aforementioned problems of motor overload can occur.
U.S. Pat. No. 5,462,238 describes a comminuting device with a cutter drum, where the knives of the cutter drum cut against a stationary counter knife and where two driven feed rollers in a feed funnel are arranged ahead of the cutter drum, effecting a uniform forced feed of insulating material to the cutter drum. The comminuted material is transported by a screw conveyor downstream of the knives of the cutter drum and freely exits in axial direction from the casing tube of the cutter drum.
A processing of large solid or packet-like chunks of plastic is not possible with this feed roller arrangement, because either a blockage or an overloading of the apparatus occurs and also the feeding of the comminuted material to a screw conveyor is not possible with this comminuting apparatus.
The description in the printed patent document WO 93/25312 concerns an apparatus for comminuting and plasticizing of thermoplastic material with two cutter drums furnished with knives engaging into each other, the knives pulling in the material, comminuting the material and stuffing it downward into a screw conveyor aligned on a common axis. The cutter drums employed in this arrangement have the disadvantage that the material to be processed may not consist of overly thin parts or overly small parts nor of large solid pieces such as molten cakes, because this will result in either an overloading of the extruder or of the cutter drum drive or a blockage of the apparatus.